If you bought from ebay i assume its second hand???
I had a 3870 XT GDDR4 which i got from ocuk but after about 3 years it just packed up. i removed the fan to see if there was a heating issue and found a whole pot of gunk covering everything underneath the heatsink. I removed it all and put on a more sensible amount but this didn't help. I tried driver installs and CCC updates but nothing works. In the end i got myself a nice new 5770 PCS+ which works just fine.
If nforce4max's idea doesn't work then you should try to RMA like he said of just get a new one. To buy a 3870 X2 with todays market seems a bit strange when you can buy a more future proof 5XXX card with similar / better power at just a little extra.
Well I run a few older games that it actually works better on, but in CCC the option for crossfire is not available (darkened out). As far as ebay, it was a pretty good deal for how well it does versus how much some of the other newer cards are.
I guess I'll have to try option one and see if there is too much goop on the card.
Hmmm see if the ports from the second gpu are working or not throwing arctifacts if it is RMA it. As one had already clean the cooler since this card does run on the hot side. The PLX chip could be at fault here.